Spectroscopic apparatus



Feb. 29, 1944.

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Patentedl F eb'. 29,1944

2,342,5137 SPECTROSCOPIC APPARATUS V Samuel J. Jacobsohn, Chicago, Ill.. assignor to The Gaertner Scientific Corporation,

ration of Illinois VApplication March 14, 1941, Serial No. 383,405

6 Claims.

This invention relates to spectroscopic apparatus, and more particularly to a spectrograph and a monochromator. 'I'hat is, this invention relates to lightv dispersing apparatus adapted to be used in combination with photographic means for recording the lines and bands of the spectrum, or in 'conjunction with means for selecting and isolating 'a particular line or band of the spectrum, sometimes used with further means for measuring the intensity of the line or band.

One feature of -this invention is to provide ya spectroscope of suchA accuracy that it is possible to perform accurate quantitative analysis therewith. Another feature is to provide a highly accurate spectroscopeof relatively small dimensions; Still another feature is to provide a spectrograph which may be handled by a single operator, wherein the dispersed light is received on aphotographic plate positionedgadjacent to the light source. Yet anotherv feature is the provision of a mirror in the optical train of a spectroscope. vA further feature is the adjustment of a spectroscope to expose apredetermined light path to various parts of the spectrum while at the same timemaintaining the accuracy of the focus thereof. Another feature is to provide compensation for the variations of the focus of rays of different wave lengths by the quartz 'optical parts usedln the spectroscop'e. Stili a further feature is the development of independent means for guiding the movement of each of the adjustable optical parts of the spectroscope. 'Yet another feature is the provision of adjustable. means for providing :minute variations in the movement of a part. A further feature is the modification of a highly accurate. spectroscope for use as a monochromator. The word spectroscope is used throughout this specification and the appended claims in a Vgeneric sense including spectrographs and monochromators.-

Other features and advantages will appear from the following 4specification and drawings, in which: f 1

Figure 1 is a side elevational view of the spectro- -grapm Figure 2 is a similar view of'the work holder and light source for the spectrograph, this i ngure being a continuation of Figure 1; Figure 3 isspianviewofthespectrograpml'igureiisa vertical sectional view,- taken along the "line 4 of 'Figure 3; Flgure-5 is a sectional view, taken along-the line l of Figure 1; Figure 46 is a sectional view of the portion o'f' the' apparatus with the upper portion thereof removed; Figure 8 is a fragmentary detail plan view of the guiding means for the mirror arm; Figure 9 is a view taken along the line 9 9 of Figure 8; Figure ,10 is a fragmentary sectional View, taken along the line i0 of Figure 8; Figure 11 is a vertical sectional view, taken along the lineil of Figure 6; Figure l2 is a fragmentary detail sectional view, taken along the line I2 of Figure 7; Figure 13 is a vertical sectionalview, partly broken away, taken along the line .I3-i3 of Figure 12; Figure 14 is a side elevational view of the plate holder mechanism; vFigure 15 is a vertical sectional view, taken along the line i5 of Figure 14; Figure 16 is a transverse sectional view, taken along the line i6 of Figure 14;`Figure 17 is a'schematic illustration of a modification of the apparatus; Figure 18 is a fragmentary vertical view of the plate holder end of anothermodication of my spectroscope; Figure 19 is a side elevational view particularly showing the adjusting and locking means for the y plate holder; Figure 20 is a fragmentary horizontal plan view of the principal working parts of. the modified form of my spectroscope, the casing being in section; and Figure 21 isa sectional view along the line 2| of Figure 20, with the lens mounting omitted.

The apparatus may be used 'with conventional equipment for providing light to be analyzed, as by activating a material to cause the emission of light therefrom, o r passing light through translucent material to be modied thereby. 'I'he light is received within the apparatus, analyzed or dispersed, and may be delivered to aphotographic plate. If the exposure of the plate is made for a predetermined time, lthe density of the lines on the photographic plate may be used to measure quantitatively the proportion of the various lines of the spectrum present in the emitted light. From' this measurement it is possible to determine quantitatively the amount of a particular element prsent in the original material.

' Where quantitative analysis may be accomplished by consideration of individual lines, the apparatus may b e adjusted so that the particular line or band of the' spectrum characteristic of that element will be cast on an aperture or slit which is substituted for the photographic plate. The intensity of the light passing through the aperture may then be measured by means of a photoelectric cell and an electrometer. From this measurement the quantity of the element or compoimd in question may be determined.

The apparatusof course. may be used for the usual purposes of a spectroscope, spectrogra-ph.

or monochromator, in addition to its use for quantitative analysis.

In the specific embodiment of the invention illustrated in Figures 1 to 16 a light-analyzing assembly A is associated with a plate holder assembly B, equipment C for holding the work and providing a light source being positioned adjacent such assemblies. An indicator screen mechanism D shows the portion oi' the spectrum which is being received on a photographic plate, or the line passing through the exit slit, where the device is being used as a monochromator.

The apparatus is carried on a frame I8 which is equipped with a support and with adjustable supports I2. ySimilar adjustable supports i8 and I4 are mounted on the frame I 8 of the mechanism C; A casing I8, supported on the frame I8,

be used for providing a desired intensity of light,

and for keepin'g the intensity standardized. From the work holder I1 the light emitted from the material passes through a pair of lenses |8 and I8 and an apertured rotatable disk 28.

The frame I8 of the mechanism C is equipped with a way or rail |80 which slidably receives the bases 2|, .22, 23 an 24 of the work polder, lenses, and disk support respectively. Locking thumb screws 28, 28, 21 and 28 serve to secure the bases in position on the rail |88. The base 24 supports a motor 28 which drives the apertured disk 28.# The lenses I8 and I9, as is usual in such constructions, are adjustable as to position with respect to the work holder l1.

The light emitted from the heated material passes through the lenses I8 and I8 and the apertured disk 28 to the analyzing assembly A. As seen particularly in Figure 3, the casing I8 joins a casting 8| which supports a housing 82. Within the housing 82 a tube 88 is mounted for longitudinal sliding motion adapted to be effected by rack and pinion means operated by the pinion head 88a, and tobe clamped in any desired position by rotation of the stud 84. Any suitable or conventional means may be used in conjunction with the tube 88 to provide an aperture or slit adjustable in size both as to width and length. If desired, a pair of spaced jaws may be used for this purpose, the space between the laws being regulated by the micrometer adjustment 88, and the angular location of the slot by adjusting means 88a. The end of the tube 88, over the laws, is preferably equipped with a quartz dust cover 88.

The casting 8| supports a plate 81 having therein an opening 88, now referring to Hgure 4. A shutter (not shown) of conventional construction in photographic equipment may be placed between the plate 81 andthe casting 8|. The shutter is controlled by 8 plunder 3l in im 100' tromagnet 48 which is operated by any suitable current supply entering the electromagnet through the wire 4I. Conventional remote oontrol means (not shown) may be provided for the electromagnet. As seen from the dotted line in Figure 6, the light beam passing through the aperture in the tube 88 traverses a path through a collimator lens 42, a prism 48, a camera lens 44 and upon a mirror 48, being reflected -by the mirror hackwardly along a path nearly parallel to the path through which the beam enters the apparatus.-

A base 48 is 'mounted on the frame I8 and in turn serves as a mounting for a carriage 41 which slidably engages the base. A plate 48 is secured to the carriage 41 by bolts 48. On the plate 48 is mounted a support member 88 for the co1- limator lens 42, the support 88 being of the usual construction for such purposes. At one end the carriage 41 serves as a mounting for a plate 5I which provides a bearing 82 for the pivotal mounting of the arm 88. The other end of the arm 88 is equipped with a support 84 for the mirror 48.

Referring now to Figure 11, the plate 48 is equipped in the central portion thereof with a stirrup 88 and an upward extension 58. The stirrup and extension serve as mountings for the hearings 81 and 88 in which the shaft 88 is carried. The shaft 88 in turn supports a member 88 which carries the prism 48, the prism being held in place in the member by thumb screw 8|. The stirrup 88 and extension 88 also support the bearings 82 and 88 for the shaft 84 which carries a mounting 88. A lateral extension 88 of this mounting carries a support 81 for the camera lens 44, the wholeassembly being adapted for pivotal movement about the axis of the shaft 84.

As seen particularly in Figure 7, the shaft 89 and the bearing 81 are attached to an arm 88 which extends laterally therefrom. At the other end of the arm 88 is provided a depending roller 88 and a smaller roller 18 secured to the arm 88 by the pivoted link 1I. The two rollers may be disposed on opposite sides of a cam 13 on the base 48. the rollers being urged into yielding engagement with the cam by the spring 12.

Similarly the shaft 84 and the bearing 62 are attached to an arm 14 which carries at its end a 4 dependim roller 18. A smaller roller 18 is secured to the arm 14 by the pivoted link 11, the vrollers being held in engagement with a cam 19 on-the base 48 by the spring 18. Referring again to Figure 11, the mirror supporting arm 88 is equipped with rollers 88 which ride on the plate 8| on the carriage 41 (Figure 6). `A depending shalt 82 is attached to the arm 88, and, as seen in Figure 9. is equipped with an annular flange 88 and mounted in a bearing 84. The lower end of the shaft 82 is threadedly engaged by a collar 88 cooperating with the bearing 88 to hold the shaft in place.

A sleeve 81 extends around the bearings 84 and 88 and is equipped with a laterally extending arm 88.v To the lowerv portion of the shaft 82 is attached, by any suitable means, the roller 88 on the ring bearing 88. the roller 88 being eccen- 'tl'iiiy disposed with respect to the axis of the 'shaft 82. This roller 88 is adapted to engage the cam 8| and thus guide the movement of the mirror supporting arm. A plate 82 extends across the cam 8| and is providedwith a pair of rollers 84 at one end and an opening 88 at the other end.

` The opening 88 is larger than the lower extension of the shaft 82 which it surrounds (Figure Il). and thus may be moved horizontally away from the shaft 82. A spring 88 attached to the pin 88, operating against the base providedby the rollers 84, continuously urges the roller 88 into engagement with the cam 8|, the opening 88 providing suilicient play of the associated part oftheshaft.

As may be best seen in Figure 8, the laterally extending arm 88 is provided with a roller 91 and with a lever 38 pivotally mounted on the arm at the point 99. .The lever 98 in turn carries a roller which is urged into engagement with the flexible strip |02 by the spring clip |0I.

The flexible strip |02 (Figure 6) is supported between the bolts |03 in the bars |04 and |05 so that anyportion of it may be adjusted as to lateral position by movement of these bolts. Because of the eccentric mounting of the roller 89, movement of the strip |02 causes the position of the arm 53, and thusof the mirror, to be changed. Moreover, the arm 88 provides motion reduction so that a given' adjustment of the cam surface shape provided by the flexible strip results in a reduced change in the mirror position. This provision of an adjustable cam is particularly important in that it enables adjustment at any' time to compensate for variations in the apparatus.

One of the critical adjustments of the spectroscope is the position of the mirror which must be so related rto the other optical elements as to reflect a definite wavelength to a definite position on the photographic plate. The required position is affected by variations in the manufacture of the optical parts. The position of the mirror as actually attained in the instrument is,

however, dependent on the length of the arm,

thelocation of the cam surface, of the pivotings, 7

etc., which likewise are subject to variations in manufacture.

It is to enable adjustable compensation for Vthese factors that the flexible cam or strip |02 is provided. In setting up the machine this flexible strip would ilrst be made straight, the theoretically ideal shape, and the machine run through its various positions. Any discrepancies in the position of the mirror at variousV points throughout its range of movement are then compensated for by movement of the bolts to change the shape of the flexible strip or supplemental cam. This supplemental cam is eective through the motion reduction means and eccentric to cause minute variations in the relation between the mirror'and its operative cam, so that relatively coarse, easily Vmade adjustments of the position of the strip |02 will result in very fine and accurate compensation for any minute variations from the proper position of the mirror.

Referring to Figure v5, the movement of the carriage 41 is controlled by the turning of the wheel |06. Motion of the wheel |06 is imparted to the shaft |01 and in turn to the gears |08 and |09 and the shaft ||0. The rotation of the shaft ||0 is carried through a. pair of universal joints and ||2 to the `shaft ||3 (Figure 7). A threaded shaft 4 is attached to the shaft ||3, the end of the shaft ||4 being supported in a bearing .4 A threaded sleeve ||6 engages the shaft ||4, and, as seen also in Figures 12 and 13,

, imparts motion to the carriage 41.

The sleeve` |6 is open on one side and is drawn into engagementwith the shaft ||4 by the bolts the casting 3| engages at one end the cam |63. The engagement is maintained by a spring |66. The other end of the lever |64 'is received within the frame |68 of the plate holder mechanism and engages the end |61 of a thumb screw adjuster |69. The plate holder frame is mounted on a bearing |23 which is adapted to rotateabout a vertical axis through the center of this bearing. 'I'hus when the wheel |06 is turned, the plate holder assembly B is rotated.

As seen particularly in Figure 15, the frame |68 of the plate holder assembly B is joined to the casting 3| by iiexible bellows |10. The casting is provided with an aperture |1| through which the light passes to the photographic plate. On the frame |68 of the plate holderassembly B is mounted a casting |12 which in turn supports the plate holder |13, the plate holder being held in position by the bars |24 and |25. The .plate holder |13 is` equipped with a cover |26 attached at one end to hinges |21. The other end of the cover |26 is provided with lugs |28 which receive the locking levers |29, the levers being pivotally mounted on the bosses |30 of the plate holder |13.

Within the plate holder is a retractable slide |3| of the type conventionally used in photographic apparatus. Behind the slde |3| is the photographic plate |32 and a support |34 therefor. A spring clip |35 holds the support |34 in position.

Referring now to 'Figure 16, the casting |12 is received within ways |36 and |31 and is equipped on the surface thereof with a pair of racks |38 and |39 which are engaged by the gears |40 and |4,|. The gears |40 and |4| are mounted on a shaft |42 driven by a gear |43 which is in turn engaged by the worm |44. A vertical shaft 45 carrying the worm |44 is driven by the bevel gears |46 and |41, the gear |41 being mounted on the shaft |48. A wheel |49 is used to rotate the shaft B58, thus imparting vertical motion to the casting |12.

The screen indicating mechanism D is shownparticularly in Figures 1 3 and l1. The mechanism includes a scale on the carriage 41, the scale being opaque except for the markings thereon. A lamp |8| in the housing |82 casts a beam of light on the mirror |83, the beam being reflected upwardly through the scale |80 to the mirror |84. From the mirror |84 ,a beam is reected to the mirror |85 and from there reflected to a translucent ground glass screen |86 upon which the scale is registered.l Movement of the carriage 41 and the scale |80 attached thereto causes the scale, as shown onthe screen |86, to move horizontally. e

In the modification of the invention shown in Figurel', a tube |81 is attached to or replaces the plate holder.

slit or aperture |88 through which a beam of ||1. An upward extension ||8 of the sleeve ||6 member assembly Bis also. moved by the operaation ofthe wheel |06. I The worm-IGI on the shaft v|| 0 drives a Vgear |62 which carries acam |63. A lever-|64 vpivotally-mounted at.l |65 on light may pass. The beam of lightpassing through the aperture |88 is received in a photoelectric cell assembly|89 and converted into electrical energy. The current .generated by the photoelectric cell may be` measuredfby .an electrometer |90 of the .usual construction, theelectrometerbeing connected tothecell assemblyby wires |9| and |92. l Itis thus vapparent thata direct reading maybe made ,of theintensity 'of any gven line or,A band inthe spectrum;v and where the intensity of v the-lightemitted from the source is standardized, this provides information as to the material',beingaactivated'by,thearc.

The 'tube' is equipped with` a To describe the operation of the apparatus, a material 30 to be analyzed is heated or electrically excited in the usual manner in the work holder I1. The light emitted from the material passes through the lenses I8 and I 6 and then `through the apertures in the rotating disk to the slit or aperture in the tube 33 and thus into the casing |6. The path which the light travels in the casing I6 includes the opening 38 in the plate 31, the collimator lens 42, the prism 43, and the camera lens 44. From the lens 44 the light passes to the mirror 45, from whence it is reected to the photographic plate |32. In order that diiIerent wave lengths of light may be simultaneously focused on the photographic plate, the plate is set at an angle with respect to the path of the light. To obtain proper focusing of the light, the camera lens 44, the mirror 45 and the photographic plate |32 are so spaced from each other that the distance between the camera lens and the plate along the path which the light traverses to the center of the plate is equal to the distance from the slit or aperture in the tube 33 to the collimator lens 42.

The slide |3I and the diaphragm in the plate 31 are operated in the usual and conventional manner for photographic apparatus.

The scale |80, as reflected on the ground glass screen |86, indicates the portion of the spectrum which is being received on the photographic plate |32, and also the wave length falling on the center of the plate. The scale may be empirically calibrated in terms of angstroms in orde;` that a direct reading of the light wave lengths may be made.

The photographic plate |32 may be exposed to different portions of the spectrum by rotating the prism 43. This is accomplished by turning the hand wheel |06 which, through the movement of the gears |08 and |03, causes rotation of the shafts ||0, ||3 and ||4. The rotation of the shaft |`|4 in turn causes longitudinal movement of the sleeve |I6which engages the carriage 41. As the carriage 41 moves longitudinally along the frame, the roller 63 moves along the cam 13 in engagement therewith causing rotationV of the prism 43.

Movement of the carriage 41 also causes the l vplate |32 is rotated about the axis of the bearing |23. This rotation results from the rotation of the worm |6| arid gear |32 when the wheel |06 i5 turned. The lever |64 is moved by the cam |63 on the gear |62, thus rotating the frame |83 in which the photographic plate |32 is carried. The photograp c plate |32 is not displaced; but is merely rota about the vertical axis of the bearing |23. Because of this automatic compensating rotation o! the plate |32, it is possible to obtain a camera focus of the di'erent wave lengths of light to which the plate is exposed.

The prism 43. the camera lens 44, the mirror 45, the photographic plate |32 and the various supporting arms and cams therefor are so arranged and constructed that the distance between the camera lens 44 and the photographic plate |32 along the path of light to the center of the plate remains substantially equal to the distance between the aperture in the tube 33 and the collimator lens regardless of the movement of the various members.

The mirror supporting arm 53 may be ad- Justed as to position by moving the flexible strip |02. This is accomplished by adjusting the bolts |03 in the bars |04 and |05. The movement of the rollers 91 and |00 engaging the strip |02 causes the eccentric roller 83 to be turned and the shaft 82 and arm 53 to be displaced. This adjustment is, of course, a very fine adjustment and need ordinarily only be used at the time the apparatus is first set in operation.

Micrometer adjustment of the inclination of the photographic plate |32 may also be accomplished by turning the thumb screw |69 in the frame |68.

With this instrument a quantitative analysis may be made by merely exposing the photographic plate to the spectrum for a predetermined length of time. By using the instrument with materials of known composition, an empirical calibration for the various light intensities may readily be made. When the plate is then exposed to the spectrum from a material of unknown composition, the analysis of the material may readily be calculated from the intensity of the spectrum bands on the photographic plate.

'I'he photographic plate |32 is preferably of such a size that two or more exposures may be made thereon by merely shifting the position of the plate. The vertical position of the plate may be shifted by turning the hand wheel |49 which causes rotation of the gears |41 and |46 and the worm |44. As a result, the gears |40 and |4| are rotated and the casting |12 is raised or lowered in the ways |36 and |31.

The operation of the modification of the instrument shown inFigure 17 is substantially the same as that of the preferred embodiment except that an aperture |86 is substituted for the photographic plate |32. The instrument is then adjusted by means of the hand wheel |06 so that a predetermined band of the spectrum is cast on the aperture |88. The intensity of this band is then determined by exposing a photoelectric cell to it for a predetermined length of time, the current generated by the photoelectric cell being measured by means of an electrometer or other suitable means.

Turning now to the modification or form of my invention shown in Figures 18 to 21, this is a simplified form of spectroscope having practically all of the desirable features of my preferred spectroscope heretofore described. The principal diiference between this and the earlier described form of spectroscope is that in the modification now to be described only a given predetermined number of positions of the parts are provided. That is, instead of apparatus for maintaining coordinated positions of the various movable parts through any range of positions, the arrangement is such as to provide a given number (here shown as five) positions of the parts, all of the parts being properly coordinated in any one of the given positions.

Referring first to Figures 18 and 19, the means for adjusting the plate holder will be described as illustrative of the means foi properly locating and locking all of the movable elements of the spectroscope. As in the other modification of my invention, the base 200 has a plate holder 20| pivotally mounted thereon, apparatus includingl the manually rotatable wheel 202 also being pro.- vided to enable two or more exposures to be made on one plate. The plate holder is carried on what may be termed a mounting plate 203, thisV mounting plate being rotatably slideable over a base plate 204 mounted on the trarne 200.

As may be best seen in Figure 18, the mounting plate 203 has a slot 205 therethrough cooperating with the thumb screw or locking means 208, this part being threaded into the plate 204. T he plate 203 is also provided with a plurality of holes adapted to register with holes in the plate 204 in various positions of the mounting plate 203. These holes are here shown as five in number, since it has been found that the entire visible spectrum and the useful portion of the ultraviolet can be properly covered by ve different positions of the spectroscope elements. The use of a plurality of different cooperating holes, of course, is to enable the use of larger holes than would be possible in view of the limited movement of the plate 203.

The parts are shown as yproperly vlocated and locked in what is here arbitrarily termed the number iive position. This is effected by manuare all properly coordinated and the desired portion of the spectrum is thrown on the plate with ally pushing a' dowel pin 201 through a hole in the plate 203 and into a cooperating hole in the plate 204 when these holes register, as indicated in Figure 19. Forcing the slightly tapered dowel pin down insures proper registry of these number ilve openings; and then the plates can be locked in this position by tightening of the thumb screw 206. This results in very convenient and accurate location and locking of the movable plate holder in one of the five predetermined positions; and movement to and locking in one of the other positions would be eifected by loosenlng the thumb screw, bringing the other openings into registry with the dowel pin therein, and then again tightening the thumb'screw.

, Turning now to Figures 20 and2i, it will be seen that all of the other movable elements of the spectroscope are adjustable to and lockable in corresponding positions. As in the rst described modincation of my invention, a carriage 208 is slideable along a base provided by rails 209 and 2I0, this enabling movement of the collimator lens 2|| toward and awa'y from a light source, not shown in this view. Light passing through the collimator lens strikes the prism 2 I2, as before, and is dispersed into a spectrum, at least part of the spectrum then passing through the camera lens 2|3 and striking the mirror 2|4 to be reilected back to a photographic plate in the holder 20| adjacent the light source, or to a selector slit and electric measuring means where the device is used as a monochromator. The carriage, as mentioned above, is slideable toward and away from the light source; the prism 2|2 is pivotal about the axis 2li; the camera lens 2|3 is mounted for pivotal movement about the a`xis 2|6; and the mirror 2I4 is supported on an arm 2|1 pivotal about the axis 2I8. As b'efore,

these movable parts, and the rotatable plate' holder, form five movable elements of the spec'- troscope system, and their respective positions must in all cases be coordinated. Instead of being synchronously movable by a single manual means, the various elements in this last modification are all independently movable. However, means for indicating when the elements are in a predetermined position, and locking them in that position, are provided so that if each of the elements is in what may be termed number five position, as illustrated in these.drawings, they optimum optical results.

In order to locate and lock the carriage in place `on the rails, two thumb screws 2|! and 220 are adapted to cooperate with two dowel pins 22| and 222. In order to insure against any side play or movement of the carriage on its ways, two locking thumb screws and dowel pins are used, so that the associated holes are duplicated at each end of the carriage and on the associated rail 209. As stated before, the carriage is shown in number ve position. If it is to be moved to number one position the thumb screws 2|9 and 220 are screwed out of their associated threaded holes in the rail 200, and the dowel pins 22| and 222 pulled out. The carriage is then manually slid to the left until the opening 223 in the carriage (the numberone opening) is in registry with the opening 224 in the rail, and the dowel pin 22| is then slipped into place. `Any slight movements necessary to register opening 225 at the other end of the carriage with opening 226 in the rail is then made, andthe dowel pin 222 slipped into these openings.4 The carriage is then locked in place by threading the thumb screws 2|0 and 220 into the openings 221 and 228 and tightening them down. Intermediate .positions of the carriage, arbitrarily identified as positions two, three and four, can lbe similarly accurately located and the carriage locked therein.

While the other movable elements are also here shown in number iive position, they could be similarly coordinated with the carriage in number one position. With respect to the prism 2|2, this would be effected by loosening the thumb screws 229 and 230 to rotate the plate 23| carrying the stirrup in which the prism 2 2 is mounted. The plate 23| is provided with five openings adapted to register with ilve cooperating openings in the base plate 232; and to effect proper location of the prism in number one position the dowel pin 233 would be withdrawn from the position shown and moved into the holes at the other end of the line, it'being assumed that the plate has been manually moved to such a position as to bring these holes into registry. Similarly, movement of the camera lens 2|3 would be effected by loosening the thumb screw 234, withdrawing the ,dowel pin 235 from the hole in which it is shown, manually moving the camera lens until the holes at the other end of the cooperating lines of holes are in registry, inserting the dowel pin, and tightening the thumb screw 234. Movement of the mirror would be effected by withdrawing dowel pin 236 from the hole in which it is shown, `moving the arm 2|'I until the opening 231 in the plate 238 is in registry With the opening 239 in the plate 240 on the carriage, and again inserting the dowel pin.

It will be apparent that accurate settings in intermediate positions (speaking of the positions arbitrarily identiiied as'2, 3 and 4) could be similarly effected, so that there would be five sets of coordinated positions for the live movable -ments by a single manual operation, it does give a very simple and easily operable method of securing coordmated positions of the elements,

While I have described and shown certain emv bodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

1. Spectroscopie apparatus of lthe character described, including: an entrance slitta nonachromatic quartz collimator lens mounted in the path of light from said slit; a light-dispensing quartz prism for receiving light from said lens; a non-achromatic quartz camera lens adjacent said prism to receive dispersed light therefrom, a mirror mounted adjacent said camera lens and adapted to reflect the light back to a terminal point adjacent the slit, whereby the dimensions of the apparatus are reduced for a given focal length, there being only a single such optical system and the light passing through each optical element thereof only once in its path from the slit to the terminal point; a single carriage movable toward and away from the slit and terminal point to enable adjustment of the distance of the carriage therefrom in accordance with the different focal lengths of a non-achromatic lens for light rays from different portions of the spectrum, and carrying the collimator lens, prism, camera lens, and mirror, the prism, camera lens and mirror being rotationally mounted on thecarriage; and a separate cam and cam follower associated with each of thethree last mentioned movable elements for effecting simultaneous rotational movement thereof in coordinated relation upon movement of said carriage, the 'various movements being so coordinated that the distance from the slit to the collimator lens is always equal to the distance traversed by light, of a median wave length of the portion of the spectrum being examined, between the camera lens and the terminal point.

2. Spectroscopie apparatus of the character described, including: an entrance slit; a nonachromatic quartz collimator lens mounted in the path of light from said slit; a light dispersing quartz prism for receiving light therefrom; a non-achromatic quartz camera lens; a mirror adapted to reflect light back to a terminal point adjacent the slit, whereby the dimensions of the apparatus are reduced for a given focal length, the lens and mirror being optically aligned in the path of light from the prism, the camera lens being adjacent the prism, vthere being only a single such optical system and the light passing through each optical element thereof only once in its path from the slit to the terminal point; translationally movable mounting means carrying the collimator lens, prism, camera lens and mirror, for simultaneous and similar movement toward and away from the slit and terminal point, the prism, camera lens and'mirror being rotationally mounted on said moimting means; and means eilectng simultaneous rotational movement of the three last mentioned movable elements in coordinated relation upon translational movement thereof in accordance with variations in the focal length of the optical system for a median wave length of the portion ofthe spectrum being examined, the various movements being so coordinated that the distance from the slit to the collimator lens is always equal to the distance traversed by light of such median wave length between the camera lens and the terminal point.

3. Spectroscopie apparatus of the character described, including: an entrance slit; a nonachromatic collimator lens mounted in the path of light from said slit; a light-dispersing prism for receiving light from said lens; a non-achro matic camera lens adjacent said prism to receive dispersed light therefrom; a mirror mounted adjacent said camera lens and adapted to reflect the light back to a terminal point adjacent the slit, whereby the dimensions of the apparatus are reduced for a given focal length, there being only a single such optical system and the light passing through each optical element thereof only once in its path from the slit to the terminal point; a single carriage movable toward and away from the slit and terminal point to enable adjustment of the distance oi the carriage therefrom in accordance with the different focal lengths of a simple lens for light rays from diiferent portions of the spectrum, and carrying l the collimator lens, prism, camera lens, and mirror, the prism, camera lens and mirror being rotationally mounted on the carriage; and means associated with each of the three last mentioned movable elements for eecting simultaneous rotational movement thereof in coordinated relation upon movement of said carriage, the various movements being so coordinated that the distance from the slit to the collimator lens is always equal to the distance traversed by iight. of a median wave length of the portion of the I spectrum being examined, between the camera lens and the terminal point.

4. spectroscopic apparatus of the character described, including: an entrance slit; a nonachromatic oollimator lens mounted in the path of light from said slit; a light-dispersing element; a non-achromatic camera lens; a mirror adapted to reflect the light back to a terminal point adjacent the slit, whereby the dimensions of the apparatus are reduced for a given focal length, the lens and mirror being optically aligned in the path of light from the light-dispersins element, there being only a single such optical system and the light passing through each optical element thereof only once in its path from the slit to the terminalv point; mounting means translationally movable toward and away from the slit and terminal point to enable adjustment oi' the distance of the mounting means therefrom in accordance with the different focal lengths of a non-achromatic lens for light rays from diiferent portions of the spectrum, the mounting means carrying the collimator lens, light-dispersing element, camera lens and mirror, at least the light dispersing element and mirror being rotationally mounted; and means associated with each of the rotationally ,movable elements for mechanically ensuring angular positioning thereof in coordinated relation upon movement of said mounting means, the various movements being so coordinated that the distance from the slit to the collimator lens is always equal to the matically operable upon operation of the rst mentioned positioning means.

6. Spectroscopie apparatus of the character described, including: an entrance slit; an element for dispersing the light into a spectrum, said element being movable; a second element adapted to optically affect at least part of the dispersed light, said second element being rotationally movable, the position ofone of said elements being dependent upon the position of the other; means for eiecting coordinated movement of both elements by a single operating means, including a cam and a cam'follovsrerv eiecting rotational movement of said second element, the contour of the cam being so designed that said cam would effect the required rotational movement of-said second element ii each of the above-mentioned elements were optically perfect; and a second cam and a second cam follower, the second cam being adjustable to vary the relation between said second element and the first cam follower in response to movement of the first follower, adjustment of said second cam providing compensation for deviations of the op- 

